The vulcanized elastomers based on vinylidene fluoride copolymers are well known and are widely employed in a plurality of applicative fields where an exceptional chemical resistance to solvents, lubricants, fuels, acids and the like, even at very high temperatures, is required.
According to the most advanced art, for the vulcanization of the vinylidene fluoride elastomeric copolymers use is made, as vulcanizing agents, of polynucleofilic compounds and in particular of aromatic polyhydroxyl compounds (or of similar thioderivatives), either as such or in the salified form.
Such products, however, are affected by the drawback of requiring extremely long vulcanization times, wherefore they are employed in combination with substances exerting an accelerating action.
Among the substances which exert an accelerating action according to the most advanced technique there are described derivatives of tertiary amines containing four nitrogen-carbon covalent bonds, and derivatives of tertiary phosphines containing four phosphorus-carbon covalent bonds (French Pat. No. 2,091,806 and No. 2,096,115).
Compounds containing one or more carbon-nitrogen covalent bonds (U.S. Pat. No. 4,259,463) and compounds having the structure of phosphonium ilides (U.S. Pat. No. 3,752,787) are described too. One of the drawback rising from the use of such accelerators is the difficulty in obtaining a perfect homogenization of same in the blend, so that hypervulcanization phenomena or scorching, or undervulcanization phenomena take place, with consequent insufficient and non-homogeneous adhesion of the vulcanized articles to metals.